From 4afd808be7cbe3a97c41ccfd732eca9dcae0fdc4 Mon Sep 17 00:00:00 2001 From: Konstantin Belousov Date: Mon, 19 Dec 2016 22:18:36 +0000 Subject: [PATCH] Do not clear KN_INFLUX when not owning influx state. For notes in KN_INFLUX|KN_SCAN state, the influx bit is set by a parallel scan. When knote() reports event for the vnode filters, which require kqueue unlocked, it unconditionally sets and then clears influx to keep note around kqueue unlock. There, do not clear influx flag if a scan set it, since we do not own it, instead we prevent scan from executing by holding knlist lock. The knote_fork() function has somewhat similar problem, it might set KN_INFLUX for scanned note, drop kqueue and list locks, and then clear the flag after relock. A solution there would be different enough, as well as the test program, so close the reported issue first. Reported and test case provided by: yjh0502@gmail.com PR: 214923 Tested by: pho Sponsored by: The FreeBSD Foundation MFC after: 1 week --- sys/kern/kern_event.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c index b734cf271bc..e832120836c 100644 --- a/sys/kern/kern_event.c +++ b/sys/kern/kern_event.c @@ -2006,6 +2006,7 @@ knote(struct knlist *list, long hint, int lockflags) struct kqueue *kq; struct knote *kn, *tkn; int error; + bool own_influx; if (list == NULL) return; @@ -2036,11 +2037,14 @@ knote(struct knlist *list, long hint, int lockflags) */ KQ_UNLOCK(kq); } else if ((lockflags & KNF_NOKQLOCK) != 0) { - kn->kn_status |= KN_INFLUX; + own_influx = (kn->kn_status & KN_INFLUX) == 0; + if (own_influx) + kn->kn_status |= KN_INFLUX; KQ_UNLOCK(kq); error = kn->kn_fop->f_event(kn, hint); KQ_LOCK(kq); - kn->kn_status &= ~KN_INFLUX; + if (own_influx) + kn->kn_status &= ~KN_INFLUX; if (error) KNOTE_ACTIVATE(kn, 1); KQ_UNLOCK_FLUX(kq);